GEN-003, a therapeutic vaccine containing recombinant herpes simplex virus (HSV) antigens, showed significant antiviral activity lasting up to a year and reduced the number of genital herpes lesions and days with recurrences, researchers reported this week at the ASM Microbe 2016 meeting in Boston.

After prior research showed that GEN-003 reduced HSV-2 shedding and lesions, Kenneth Fife from Indiana University and colleagues conducted a Phase 2 study to confirm its activity and select the best dose combination for future trials.

Study participants collected genital swabs twice daily for HSV-2 DNA PCR testing at 28 days before vaccination, after the third injection, and at 6 and 12 months following immunization, and they were asked to record stop and start dates of every herpes outbreak.

The researchers found that 12 months after immunization HSV-2 shedding was reduced significantly -- by about 60% -- in the vaccine regimen groups receiving 60 mcg of the HSV-2 antigens and 50 or 75 mcg of the adjuvant. However, among people who received 30 mcg of the antigens, only those receiving the highest adjuvant dose showed a significant reduction.

Most of the groups receiving active vaccines -- except for the lowest-dose regimen -- had a significant reduction in herpes lesions, ranging from about 40% to about 70%. Up to a third did not experience lesion recurrences 12 months after vaccination.

GEN-003 was generally safe and well-tolerated. The most common side effects were injection site pain, fatigue, and muscle aches; 9 people discontinued due to adverse events. No severe (grade 4) reactions or serious adverse events were reported.

"GEN-003 is believed to work through a different pathway from most vaccines by recruiting T-cells, which are critical to controlling chronic infections such as herpes," Fife stated in an American Society for Microbiologypress release. GEN-003 is also designed to stimulate antibodies to help neutralize the virus.

Fife added that GEN-003 is expected to be tested in combination with antiviral medications -- such as oral acyclovir (Zovirax), famciclovir (Famvir), or valacyclovir (Valtrex) -- and could "potentially provide a level of relief not currently achievable."